In three phase power systems, the output of the power supply is characterized by the provision of three line voltages (L1, L2 and L3) of 277 volts when connected to ground or neutral. When the three line voltages are interconnected, i.e. (L1 to L2, L2 to L3 and L1 to L3) the output is 480 volts per interconnected circuit. The presence of such high voltages poses an extremely dangerous working environment.
In traditional methods for determining the active status of such three phase electrical power supplies during lock out/tag out (LO/TO) operations, a power supply that had been locked out and tagged out (LO/TO'd) was presumed to be energized until verified otherwise through some form of testing procedure or “try” process. Such testing or trying procedures are generally characterized as Mode 2 work on an energized system. Mode 2 basically consists of probing and troubleshooting activities on energized systems and is the mode between Mode 1, working on deenergized systems and Mode 3 involving manipulative work on energized systems. The testing or “try” processes often involve actual opening of the power supply enclosure and exposing the operator to any potentials or other hazardous conditions that may exist inside of the enclosure.
The availability of an apparatus or system that obviates the need for such Mode 2 activities would significantly reduce the possibility of operator exposure to residual potentials or other hazardous conditions that might exist inside of a power supply enclosure.
Accordingly, there exists a need for a device and methods that provide a fail safe indication of the absence of potentials within a power supply enclosure without the need for Mode 2 activities to make such a determination before further maintenance or other activities are performed on the power supply within the power supply enclosure.